Here are some solved questions from TCS Placement Papers

1) Find the smallest number such that if its rightmost digit is placed at its left end, the new number so formed is precisely 50% larger than the original number.

Answer
The answer is 285714.

2) There is a 4-character code, with 2 of them being letters and the other 2 being numbers.How many maximum attempts would be necessary to find the correct code? Note
that the code is case-sensitive.

Answer
The maximum number of attempts required are 16,22,400

3) How many possible combinations are there in a 3x3x3 rubics cube? In other words, if you wanted to solve the rubics cube by trying different combinations, how many might it take you (worst case senerio)?How many for a 4x4x4 cube?

Answer
There are 4.3252 * 10^19 possible combinations for 3x3x3 Rubics and
7.4012 * 10^45 possible combinations for 4x4x4 Rubics.

4) There are 20 people in your applicant pool, including 5 pairs of identical twins.If you hire 5 people randomly, what are the chances you will hire at least 1 pair of
identical twins? (Needless to say, this could cause trouble ;)

Answer
The probability to hire 5 people with at least 1 pair of identical twins is
25.28%